Science across the curriculum.0:01
5 Exercise 4, page 87 1.0:04
Tornadoes Anytime, any place Tornadoes are one of nature's most violent storms, and they happen in various parts of the world.0:17
They can form at any time of the year, although many occur in the spring.0:41
Round and Round A tornado is a spinning, whirling wind.0:47
When it meets with cold air, it takes the shape of a long funnel or tube reaching down from a large cloud.0:53
It is formed when warm air near the Earth's surface rises and meets with cold air.1:01
When the weather conditions are right, this warm air starts to twist as it rises, getting faster and stronger.1:08
It is a bit like watching water disappear down the plug hole in your bathtub.1:17
If this huge twisting rope of air hits the ground, it may cause great damage.1:22
Tornadoes can reach speeds of more than 250 miles per hour, ripping roofs from houses, uprooting trees, and tossing heavy objects like cars in the air.1:29
Measuring strength in 1971, a meteorologist named Theodore Fujita developed a scale to show how strong tornadoes are.1:43
His scale goes from F0 to F5.1:55
It doesn't calculate strength based on wind speeds, but the damage a tornado causes to homes and other buildings.2:00
Hail different sizes Hailstones are lumps of ice.2:33
They can be as small as peas or as big as cricket balls.2:39
In Kansas, USA, a hailstone fell and that was 44.5cm across.2:44
Getting ready to Drop Hail is formed when raindrops start to fall.2:53
Before they reach the ground, they are blown up into the clouds again by strong winds.2:59
There they freeze into balls of ice, and the wind in the clouds bounces them up and down.3:05
As the frozen raindrops rise and fall like this, they get even more thickly covered in ice from the water inside the clouds.3:12
Eventually, they get so heavy that they fall to the ground as hail.3:22
Easy to hear when big hailstones fall, they make quite a noise, hitting roofs and pavements.3:28
Cars and buildings are damaged and plants and crops are destroyed.3:36
Driving during a hailstorm is is also very dangerous as the roads become slippery.3:41
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